The present invention relates, in general, to the field of laser rangefinding and speed measurement instruments. More particularly, the present invention relates to a pseudo-stabilization technique for laser-based speed and rangefinding instruments utilizing a rate gyroscope to track the instrument's aiming point and increase the effective range of the device by enabling the placement of a greater percentage of higher power pulses at a higher pulse rate on target while concomitantly adhering to Class 1 eye-safety standards.
Laser rangefinders, such as those designed and produced by Laser Technology, Inc., Centennial, Colo., assignee of the present invention, operate to calculate distance by measuring the time of flight of very short pulses of infrared light. That is, a measurement is made as to the time it takes one or more laser pulses to travel to a target and back with a precision time base. With knowledge of the constant speed of light, the distance the laser pulses have traveled can then be calculated.
In order to increase accuracy, such laser rangefinders are designed to process multiple pulses in a single measurement period, with target acquisition times typically ranging from 0.3 to 0.7 seconds. Sophisticated accuracy validation algorithms are then utilized to ensure reliable distance measurements and eliminate spurious signals due to noise and other factors.
Laser Technology, Inc. has pioneered and developed the design and measurement functionality found in some of the most popular lines of rangefinders and speed measurement instruments currently available on the market. Representative of its proprietary technology is that disclosed in U.S. Pat. Nos. 5,574,552; 5,612,779; 5,652,651; 5,703,678; 5,880,821; 5,926,260; 6,057,910; 6,226,077 and 6,445,444, the disclosures of which are herein specifically incorporated by this reference in their entirety.
Laser-based speed and rangefinding instruments have to adhere to strict eye-safety standards and consumer devices in particular have to adhere to U.S. Food and Drug Administration Title 21 and International Electrotechnical Commission (IEC) 60825 Class 1 standards. These regulations define a 514 nanojoules per pulse energy maximum. In reality, this figure must then be further reduced and divided by the fourth root of the number of pulses emitted in the applicable time base, which is typically just over ten seconds, thereby reducing the number further. In addition to this are the inevitable correction factors which must be accounted for such as αmin (alpha min; the angular subtense of a source below which the source can be effectively considered as a point source), beam exit size and the like. All these factors go into a determination of the limit of the nanojoules per pulse that are allowed in order for the instrument to remain within the Class 1 limits.